1. Field of the Invention
This invention relates to rubber compositions and more particularly to such a composition having improved processability and quality characteristics prior to and after vulcanization.
2. Description of the Prior Art
Ethylene/alpha-olefin rubbers, sometimes including an unconjugated diene or dienes, are usually called "EP" type rubbers and known for their great ozon resistance, high weather-proofness and superior thermal stability. Such rubbers find extensive application to automotive parts, building components, industrial rubber products and the like. EP rubbers, however, are not totally satisfactory with respect to roll retention and also to tackiness in an unvulcanized state, leading to processing inconveniences.
By the term roll retention is meant the ability of an EP rubber to adhere to the surface of a roll mill while being blended with additives. Insufficient roll retention literally entails increased labor and time in the blending.
Tackiness is an adhesive property by which a rubber in bonded to a rubber or to a different material under pressure. For instance, automotive tires or tubes are generally formed by joining rubber/rubber laminates into a desired shape which is subsequently vulcanized. Laminates of less tacky, unvulcanized rubbers are difficult to vulcanize while retaining the predetermined shape, the resulting vulcanizate being susceptible to delamination.
To cope with this problem, a variety of tackifying agents have been proposed but with no appreciable success. Cumarone resins, terpene resins and aliphatic petroleum resins known in common use as tackifiers are inadequate in tack strength. Extender oils if added in large amounts may improve tackiness to some extent, but would often render the vulcanizate physically weak. There is still much to be desired despite many attempts made with certain other types of tackifiers as disclosed for instance in Japanese Patent Publication No. 46-21897 and Japanese Patent Laid-Open Publication No. 51-87555.